The project will be conducted during 12 weekend shutdowns through the end of 2013.

The line's Greenpoint G Tube links Long Island City in Queens with the Greenpoint section of Brooklyn and it was one of nine under river subway tubes flooded during Sandy. The tube was slammed with three million gallons of salt water at the height of the storm, leaving tracks submerged and the tunnel's pump controls, electrical, communications, fan control and signal equipment seriously damaged.

Immersed in salt water, power cables are corroding from the inside, while corrosion on the outside of rails and fasteners increases the potential for short circuits, which can result in signal problems. The controls for ventilation, lighting and communication systems were destroyed and have not been restored to their pre-Sandy condition. With reliability of some components declining, they must be replaced before they become a safety issue.

During the weeks after Sandy, temporary repairs were made to the Greenpoint G Tube, which allowed G train service to resume. Components were cleaned, inspected and approved for service, but given the extent of the damage, their useful lifespan was significantly shortened and their operation degraded, leading to an increased number of failures and delays for customers.

"Work to the Greenpoint G Tube cannot be put off. This is work that must begin now. While our customers will suffer some inconvenience, the payoff will be completion of this necessary work in the shortest time possible," said New York City Transit Acting President Carmen Bianco.